(1) Field of the Invention
The present invention relates to a process for manufacturing a porous polymer having many voids in its interior, in particular a porous polymer having small apparent specific gravity and being superior in terms of water-absorbing properties, permeability and elasticity. The present invention also relates to an absorbing article such as a sanitary napkin or a paper diaper, which comprises an absorbing layer containing the porous polymer.
(2) Prior Art of the Invention
There have been known various methods of manufacturing a water-absorbing resin in which an unsaturated ethylene monomer such as acrylic acid or acrylic acid alkali metal salt is polymerized by reversed phase suspension polymerization. For example, employing reversed phase suspension polymerization or reversed phase emulsion polymerization, a polymer dispersant (disclosed in Japanese Patent Public Disclosure (KOKAI) No. 167307/1982) or a surfactant (disclosed in Japanese Patent Public Disclosure No. 32641/1983) is added to an aqueous solution containing vinyl monomer to improve the wettability of a water absorbing polymer. However, when the above-mentioned water-absorbing polymer is used, for example, as a water-absorbing agent for a sanitary napkin or a paper diaper, the water-absorbing polymer is required to have practical properties such as good elasticity, small apparent specific gravity to be easily mixed with cotton-like pulp, good water-absorbing properties and high permeability. The water-absorbing polymers manufactured by the conventional methods do not always have the above practical properties.
On the other hand, Japanese Patent Public Disclosure No. 193901/1984 discloses a process for manufacturing spherical polymer having spherical voids of an average diameter of 0.5 to 50 microns, in particular, a raw material suitable for use in cosmetics, wherein a nonionic surfactant is added to a monomer phase and an ionic surfactant is also added to a water phase in polymerization of hydrophobic monomer in aqueous dispersing medium to form water phase/monomer phase/water phase (so-called W/O/W type emulsion), after which the monomer is polymerized. However, a water-absorbing polymer having the above-mentioned practical properties cannot be manufactured by applying the above method without modification to polymerization of water-soluble monomer.